1. Field of the Invention
The disclosure relates to an image formation device and a method of controlling the image formation device, and is applicable to a color printer that performs print processing using a long medium such as a continuous sheet in the form of a large-diameter roll (hereinafter referred to as a “large-diameter roll sheet”), for example.
2. Description of Related Art
In conventional electrophotographic color printers, image formation units including LED heads, photoconductive drums, and transfer rollers have a tandem configuration in which the units of four colors, i.e., black (K), yellow (Y), magenta (M), and cyan (C) are arranged in tandem, and implement a full-color image formation by laying developer images of the respective colors sequentially one over another. Here, the developer images of the respective colors need to be transferred to the same position on a recording medium. If the transfer positions of these colors differ from one another, this entails a problem in that a color tone deviation or misregistration occurs and thus favorable print quality cannot be obtained. In conventional color printers, the main causes for defects such as a color tone deviation and misregistration are errors in the photoconductive drums and the LED heads which are replaceable parts; i.e., misalignment of the parts from their proper mounting positions, the machining accuracy of these parts, and displacement of these parts during the driving. In the conventional color printers, such errors occur while varying over time as the printer repeats printing.
For example, there is a conventional technique described in Japanese Patent Application Publication No. 2001-134041 (Patent Literature 1) to correct misregistration caused by these varying errors in the above color printers that transfer developer images of different colors one over another.
The technique described in Patent Literature 1 employs a misregistration detection pattern recognition method in which: after a sheet is delivered to the outside, a misregistration detection pattern using a black (K) developer image is transferred onto a transport belt as a base pattern; a misregistration detection pattern using a developer image of any of the colors other than black, such as colors of yellow (Y), magenta (M), and cyan (C), is transferred onto the black misregistration detection pattern while being shifted from the black pattern by predefined pitches; and the amount of misregistration is detected by using a difference in reflectance between the black image and the color image.